Tunnel forms are used to quickly and simultaneously form integral walls, floors and ceilings for tunnels from poured concrete, thus saving time and construction costs.
Tunnel forms have vertical portions connected (at the top) to horizontal portions, and can have vertically extendable or telescoping legs or feet, and cross braces and supports (props), to retain their desired configuration and orientation when concrete is poured into the vertical portions and on to the horizontal portions.
In the abstract, the process for using tunnel forms is relatively simple. Tunnel forms (with their legs or feet in a vertically extended position) are placed on the floor on both sides of a previously created starter wall (sometimes called a curb or kicker). The vertical portions of the tunnel forms are then sealed against the vertical faces of the starter wall, so that the vertical portions of the tunnel forms are coplanar (aligned) with the vertical faces of the starter wall. In this manner, the vertical portions of the tunnel forms upwardly extend the vertical faces of the starter wall, which creates a confined space between the top of the starter wall and the vertical portions of the tunnel forms. Concrete is then poured into that confined space to form a concrete wall that extends the starter wall upwards to the top of the vertical portion of the tunnel forms, and more concrete is then poured (supported by the horizontal portion of the tunnel form) to integrally form a concrete ceiling with the concrete wall. After the poured concrete has cured (dried) enough to support its own weight, the tunnel forms are stripped (separated) from the concrete wall and ceiling, and the tunnel forms are removed and reused.
Before the concrete is poured, reinforcing bar, as well as wires, pipes and other utilities, can be placed in the spaces (for the walls, floors and ceilings) defined by the tunnel forms, to be buried in the concrete and thereby incorporated into the walls, floors and ceilings. “Block outs” can also be placed in the spaces (for the walls, floors and ceilings) defined by the tunnel forms, to block out concrete from desired areas in the walls, floors or ceilings, so as to form windows and doors and other penetrations through the walls, floors and ceilings.
Tunnel forms can either be full tunnel forms, having an inverted “U” cross section, or half tunnel forms, having an inverted “L” cross section (which can be used in adjacent pairs joined at the edges of their horizontal portions to form an inverted “U”).
In actual practice, use of tunnel forms is labor intensive and therefore expensive. Conventional practice is to seal the tunnel forms against the vertical faces of the starter walls by inserting beams (usually wooden) that span the width of the tunnel being formed (between two adjacent starter walls) and then pounding those beams into place to span and forcibly spread or “smush” the vertical portions of the tunnel forms against the vertical faces of the adjacent starter walls to remove bows or wrinkles out of the tunnel form for accurate placement of block outs. To maintain this seal between the tunnel forms and the starter walls during pouring and curing of the poured cement, elongated tapered bolts (“taper ties”) are inserted at intervals (usually plus or minus 4 feet) through preexisting holes in the tunnel forms, and secured and tightened by nuts. Conventionally, an upper and a lower row of taper ties may be used, with the lower row of taper ties being subjected to greater stress from the weight of the poured concrete, so that lower taper ties may be more likely to fail. If any of the lower taper ties fails, then they must be replaced before the concrete can be poured.
Concrete is then poured into the spaces defined by adjacent tunnel forms (whose vertical portions were sealed to be coplanar with the vertical faces of the starter wall) to simultaneously create concrete walls that extend the starter wall upwards, and also to form the ceiling, which will also form the next floor above. After the poured concrete is cured sufficiently to support its own weight, rollers are placed on the floor below the tunnel forms. Then, a crane is used to support the weight of the tunnel forms, and the extendable or telescoping legs or feet are retracted. The crane is then used to lower the tunnel forms (onto the rollers), to release or “strip” the tunnel forms from the ceiling and walls formed by the cured concrete. The tunnel forms are then rolled (on the rollers) out from underneath the newly formed concrete ceiling so that they can be picked up by the crane and used again.
The labor to seal the tunnel forms against the starter walls is expensive. Likewise, the labor to remove the tunnel forms is also expensive, because the rollers must be placed on the floor, then the crane must be used to support the weight of the tunnel forms while the extendable or telescoping legs or feet of the tunnel form are retracted and to lower the tunnel forms onto the rollers, and the tunnel forms then must be rolled over those rollers. The rollers may not be perfectly aligned, or may not remain aligned as the tunnel form is rolled, so that they may need to be re-aligned as the tunnel form is rolled. The rollers on the floor also may present a safety hazard for workers. Moreover, a crane must be used to lower the tunnel forms onto the rollers, which adds significantly to overall expense.
Further, the height of the concrete walls being formed is conventionally controlled by using tunnel forms of different heights, or by raising tunnel forms from the floor by extending the extendable or telescoping legs or feet that rest on the floor. However, providing tunnel forms of multiple different heights is prohibitively expensive, because of the number of different tunnel forms that will need to be maintained. Providing extendable or telescoping legs or feet that extend sufficiently to create a range of heights increases the cost of the tunnel forms substantially, because tunnel forms are very heavy, as they must be strong enough to support the weight of concrete being poured for walls and ceilings/floors.
The following patents are considered to be background art to the present invention.
U.S. Pat. No. 6,619,885 to Pertoldi, incorporated herein by reference, discloses a tunnel form having two vertical forming walls joined by a horizontal wall, with means at the base with an amplitude of adjustment on the order of ten to twenty centimeters for adjusting the height of a top edge of the tunnel form relative to a reference surface, and means for supporting the tunnel form when the tunnel form is stripped from poured concrete, where the height adjusting means are supported by props that are slide mounted in a sleeve attached to the base of the tunnel form. A starter wall (curb or kicker) of one thousand five hundred millimeters is disclosed. The height of the walls is determined by the supports placed on the reference surface. The tunnel forms are rolled away using rollers mounted on the reference surface.
U.S. patent application Ser. No. 09/853,723 to Pertoldi, published as U.S. 2002/0166943, incorporated herein by reference, discloses a tunnel form with three forming walls, where the base and lateral edges of the form have a flat bar, and the joining and aligning means for adjacent forms are attached to the forming walls.